Re: [PATCH v6 12/19] vfio-user: IOMMU support for remote device

[Jag Raman]

> On Mar 2, 2022, at 11:49 AM, Stefan Hajnoczi <stefanha@redhat.com> wrote:
> 
> On Mon, Feb 28, 2022 at 07:54:38PM +0000, Jag Raman wrote:
>> 
>> 
>>> On Feb 22, 2022, at 5:40 AM, Stefan Hajnoczi <stefanha@redhat.com> wrote:
>>> 
>>> On Thu, Feb 17, 2022 at 02:48:59AM -0500, Jagannathan Raman wrote:
>>>> +struct RemoteIommuElem {
>>>> +    AddressSpace  as;
>>>> +    MemoryRegion  mr;
>>>> +};
>>>> +
>>>> +GHashTable *remote_iommu_elem_by_bdf;
>>> 
>>> A mutable global hash table requires synchronization when device
>>> emulation runs in multiple threads.
>>> 
>>> I suggest using pci_setup_iommu()'s iommu_opaque argument to avoid the
>>> global. If there is only 1 device per remote PCI bus, then there are no
>>> further synchronization concerns.
>> 
>> OK, will avoid the global. We would need to access the hash table
>> concurrently since there could be more than one device in the
>> same bus - so a mutex would be needed here.
> 
> I thought the PCIe topology can be set up with a separate buf for each
> x-vfio-user-server? I remember something like that in the previous
> revision where a root port was instantiated for each x-vfio-user-server.

Yes, we could setup the PCIe topology to be that way. But the user could
add more than one device to the same bus, unless the bus type explicitly
limits the number of devices to one (BusClass->max_dev).

Thank you!
--
Jag

> 
> Stefan